Display screen or a portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or a portion thereof with a graphical user interface, showing a first embodiment according to our new design; and,

FIG. 2 is a front view of a second embodiment thereof.

The broken lines showing the display screen and the remainder of the graphical user interface form no part of the claimed design. Hatched shading indicates a contrast in visual appearance. 

CLAIM The ornamental design for a display screen or a portion thereof with a graphical user interface, as shown and described. 